In general, propeller fans are axial-flow fans that include a cylindrical hub to which a rotary shaft of a driving motor is coupled and a plurality of blades extending outward from the hub to form an air flow in an axial direction. Such propeller fans have been used in outdoor units of air conditioners to force air to flow.
In this regard, the hub disposed at the center of the propeller fan receives a rotational force from the rotary shaft of the driving motor and firmly supports the plurality of blades thereby providing sufficient rigidity to the plurality of blades while the propeller fan rotates at a high speed.
However, although the hub does not make any contribution to the blowing efficiency, a relatively large size is required to support the propeller fan blades and thus the overall weight of the propeller fan increases resulting in an increase in manufacturing costs thereof.
In addition, if an angle of the blade increases to be greater than a predetermined level to increase an airflow volume of the propeller fan, flow resistance and noise may increase due to flow separation on the surface of the blade.